add openwebtext2
openwebtext2 is part of EleutherAI/The Pile, but AFAIK, The Pile dataset blend all sub datasets together thus we are not able to use just one of its sub dataset from The Pile data. So I create an independent dataset using The Pile preliminary components.

When I was creating dataset card. I found there is room for creating / editing dataset card. I've made it an issue. #2797

Also I am wondering whether the import of The Pile dataset is actively undertaken (because I may need it recently)? #1675